Patent Document 1 discloses a method of synthesizing a hydrotalcite compound which can be used as an anion adsorbent by recycling steel slag which is industrial waste. The hydrotalcite compound synthesized by this method is represented by the general formula [Ca2+a-xMxAlO3+b]Ay. When this hydrotalcite compound having this structure is calcined alone, the formed oxide agglomerates, thereby reducing activity. Since this compound has a single hydrotalcite structure, the type of an ion able to be adsorbed is limited.
Non-patent Document 1 discloses a method of treating selenium with Green Rust (GR) and a method of forming a hydrotalcite compound by using MgO as a neutralizer. To treat selenium and a fluorine ion by this method, two different types of hydrotalcite particles suitable for these treatments are required, respectively.
Patent Document 2 discloses a method of synthesizing a cleaning agent by compounding a hydrotalcite compound on the surface of magnesium oxide and a method of treating a harmful substance by using the cleaning agent. The hydrotalcite compound synthesized by this method has the same disadvantage as above.
Non-patent Document 2 discloses the synthesis of a Fe-based hydrotalcite compound and application thereof. Since the particle synthesized by this method is a single-layer Fe-based hydrotalcite compound, it has the same disadvantage as above.
Patent Document 3 discloses a method of synthesizing a Co(II)Fe(III)-LDH particle having low coercive force. The particle synthesized by this method is a Co(II)Fe(III)-LDH particle and a precursor of a CoFe-based ferrite substance. Since it has no CoFe ferrite structure, it cannot fully exhibit physical properties as a magnetic substance.
Patent Document 4 discloses a method of providing an ultraviolet absorbing function by introducing the anion of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (abbreviated as BP) between Mg—Al—NO3 type hydrotalcite layers. This method has a disadvantage that a waste liquid after exchange is colored deep yellow, whereby its treatment imposes a great burden on the environment. The method has another disadvantage that use of the particle is limited since the particle after exchange is tinged with deep yellow.
Patent Document 5 discloses a method of preparing a vinyl chloride-based resin composition for use in transparent products by mixing zinc-modified hydrotalcite and 2,4-dihydroxybenzophenone with a resin. This method is used to provide an ultraviolet absorbing function to a resin by mixing zinc-modified hydrotalcite and 2,4-dihydroxybenzophenone having an ultraviolet absorbing function. This method has a disadvantage that when time passes, an organic substance having an ultraviolet absorbing function such as 2,4-dihydroxybenzophenone is decomposed gradually, thereby deteriorating the ultraviolet absorbing function.    (Patent Document 1) WO2011/108195A1    (Patent Document 2) JP-A 2011-188651    (Patent Document 3) JP-A 2008-144412    (Patent Document 4) JP-A 2007-299039    (Patent Document 5) PCT/JP2011/063597    (Non-patent Document 1) Water treatment technique for a harmful element using an on-site forming method of a layered double hydroxide, J. Soc. Powder Technol. Japan, 50, 342-347 (2013)    (Non-patent Document 2) Synthesis and application of a Fe-based layered double hydroxide, Clay Science, Vol. 49, No. 3, p. 99-107, 2010